U.S. Pat. Nos. 3,339,499 and 3,490,387 illustrate hopper car constructions having stub sills and wherein the longitudinal loads are transmitted to the stub sill, to a shear plate, then outwardly to the side sills, and from the side sills into the car body. In accordance with the construction of these patents vertical turning moments are taken out by diagonal stiffeners at opposite ends of the car. The shear plate, side sills and the diagonal stiffeners add significantly to the weight of the car.
There is an AAR requirement that a 100 ton railway hopper car not exceed 263,000 pounds loaded. Most railroads and shippers are anxious to have a car in which they can load 100 tons of lading and at the same time not be concerned about the weight of specialty items, such as multi-wear wheels, center fillers and trucks (particularly side frames and truck bolsters) which they may wish to order with the car.
The weight of the hopper car according to the above mentioned patents for high capacity design may vary by as much as 1000 pounds or more but usually turns out to be between 63,000 and 64,000 pounds.
It therefore would be desirable to reduce the weight of the car to 60,000 lbs. and even lower, so that the user may load a 100 ton load and at the same time order the specialty items of the car which he wishes, regardless of their weight.
In application Ser. No. 439,782, filed Feb. 5, 1974, now U.S. Pat. No. 3,921,537 filed on even date herewith, a railway hopper car is disclosed in which the weight of the car is reduced through the use of a through center sill. The shear plate and diagonal stiffeners described in the aforementioned '499 and '387 patents may be eliminated. Also by the use of this through sill construction, it is possible to reduce the thickness of the side sheets and the side sill, and thus further reduce weight. In accordance with this construction it is possible to reduce the nominal weight of the car to below 60,000 pounds without controlling the weight of specialty items in the car.
Conventional through sill construction usually includes a hat shaped cross section and the use of hoods in the hoppers over the through sill to allow the lading to pass around the through sill and not be impeded thereby. This usually means that the hat-section flanges must be cut off from the through sill in the hopper area and reinforcements welded within the through sill in the hopper area. These operations require considerable man hours and are therefore expensive.
A bottom and top cover plate are generally required for the through sill at the end of the car. These plates require man hours to fabricate and weld in place.
Moreover, the bottom and top cover plates, and hoods are all weight members and it is desired to reduce as much as possible the weight of the car consistent with sound structural design.
In U.S. Pat. Nos. 1,943,294; 2,084,161; 2,519,320 and 3,040,679 it has been proposed to use a tubular center sill of circular cross section. However, the upper surface of a circular cross section has been found to be a place where some lading hangs up during unloading, and thus making a contamination problem.
U.S. Pat. Nos. 1,859,261 and 2,366,709 disclose non-circular tubes having at least five sides, making fabrication of such multi-sided tubes difficult and expensive. Furthermore, the latter with its flat lower surface results in inefficient use of space in the hoppers because a void is created during loading under this flat surface.